Catalyst comprising an active nickel phase distributed in a shell

ABSTRACT

Catalyst comprising a nickel-based active phase and an alumina support, characterized in that:the nickel is distributed both on a crust at the periphery of the support, and in the core of the support, the thickness of said crust being between 2% and 15% of the diameter of the catalyst;the nickel density ratio between the crust and the core is strictly greater than 3;said crust comprises between 40% and 80% by weight of nickel element relative to the total weight of nickel contained in the catalyst.

TECHNICAL FIELD

The present invention relates to a supported metal catalyst based onnickel intended particularly for the hydrogenation of unsaturatedhydrocarbons, and more particularly for the selective hydrogenation ofpolyunsaturated compounds or the hydrogenation of aromatics.

PRIOR ART

Monounsaturated organic compounds, such as, for example, ethylene andpropylene, are at the root of the manufacture of polymers, of plasticsand of other chemicals having added value. These compounds are obtainedfrom natural gas, from naphtha or from gas oil which have been treatedby steam cracking or catalytic cracking processes. These processes arecarried out at high temperature and produce, in addition to the desiredmonounsaturated compounds, polyunsaturated organic compounds, such asacetylene, propadiene and methylacetylene (or propyne), 1,2-butadieneand 1,3-butadiene, vinylacetylene and ethylacetylene, and otherpolyunsaturated compounds, the boiling point of which corresponds to theC5+ gasoline fraction (gasolines containing hydrocarbon compounds having5 or more carbon atoms), in particular styrene or indene compounds.These polyunsaturated compounds are highly reactive and result in sidereactions in the polymerization units. It is thus necessary to removethem before making economic use of these fractions. Selectivehydrogenation is the main treatment developed to specifically removeundesirable polyunsaturated compounds from these hydrocarbon feedstocks.It makes possible the conversion of polyunsaturated compounds to thecorresponding alkenes or aromatics while avoiding their completesaturation and thus the formation of the corresponding alkanes ornaphthenes.

Selective hydrogenation catalysts are generally based on metals fromGroup VIII of the Periodic Table, preferably palladium or nickel. Themetal is in the form of metal particles deposited on a support. Themetal content, the size of the metal particles and the distribution ofthe active phase in the support are among the criteria which have aninfluence on the activity and the selectivity of the catalysts.

The macroscopic distribution of the metal particles in the supportconstitutes an important criterion, mainly in the context of rapid andconsecutive reactions such as selective hydrogenations. It is generallydesirable for these elements to be located in a crust at the peripheryof the support in order to avoid problems of intragranular materialtransfer which may result in activity defects and a loss of selectivity.Such catalysts are also referred to as “eggshell” catalysts.

Such catalysts are widely known in the case of selective hydrogenationcatalysts based on palladium. Indeed, owing to the low palladium content(generally less than 1% by weight (1 wt %) of palladium relative to thecatalyst) and suitable preparation processes, a thin crust of palladiumat the periphery of the support grains can be obtained (FR2922784,US2010/217052).

It is often proposed to replace palladium with nickel, a metal which isless active than palladium, and which it is therefore necessary to havein a larger amount in the catalyst. Thus, nickel-based catalystsgenerally have a metal content of between 5% and 50% by weight of nickelrelative to the catalyst. In these catalysts, the nickel is generallydistributed homogeneously within the support. One possible way ofimproving these catalysts in terms of activity and selectivity is tocontrol the distribution of nickel within the support by depositing thenickel in a more concentrated manner on a crust, at the periphery of thesupport. Such catalysts are known from the prior art.

Document U.S. Pat. No. 4,519,951 describes an “eggshell” catalyst withnickel on a porous support having a pore volume of at least 0.2 ml/g forthe pores having a size of less than 11.7 nm and a pore volume of atleast 0.1 ml/g for the pores having a size of greater than 11.7 nm. Morethan 50% of the nickel is found in a crust, the thickness of which isequal to 0.15 times the radius of the support. This catalyst is used forthe hydrogenation of fats.

Document CN101890351 describes a supported nickel catalyst in which morethan 90% of the nickel is found in a 700 μm-thick crust. The catalyst isprepared using an ammoniacal solution to dissolve the nickel salt. Thesecatalysts are used in a selective hydrogenation application.

Document US2012/0065442 describes a supported nickel catalyst in whichthe size distribution of the nickel crystallites is bimodal with 30% to70% of the nickel crystallites having a mean size (diameter) of 1.0 to2.5 nm, the remaining nickel crystallites having a mean size (diameter)of 3.0 to 4.5 nm. The nickel is distributed both on a crust with athickness of 3% to 15% of the diameter and at the core, the nickelconcentration ratio between the crust and the core being between 3.0:1and 1.3:1. At least 75% of the pore volume is found in pores having asize of more than 5.0 nm.

OBJECTS OF THE INVENTION

Surprisingly, the applicant has discovered that by applying a specifichydrothermal treatment after the addition of a particular organicadditive to a catalyst based on nickel comprising an alumina supportobtained according to a very specific method, a catalyst is obtained inwhich at least a portion of the nickel is distributed over a crust atthe periphery of the support, the other portion of the nickel beingdistributed in the core of the catalyst. Without wishing to be bound byany theory, the hydrothermal treatment carried out after the step ofbringing a specific organic additive into contact with the catalystbased on nickel on a particular alumina support, having undergone ahydrothermal treatment in the presence of an acid solution, seems tocause the nickel to migrate at least in part from the interior of thesupport to the periphery of the support, thus forming a nickel crust.The present invention thus relates to a new type of catalyst which, byvirtue of its specific preparation process, makes it possible to obtaina catalyst comprising performance qualities at least as good, or evenbetter, in terms of activity and selectivity within the context of theselective hydrogenation reactions of polyunsaturated compounds orhydrogenation reactions of aromatics, while using a lower amount ofnickel phase than that typically used in the prior art, which is due toa better distribution of the nickel active phase in the support, makingthe latter more accessible to the reagents.

The present invention relates to a catalyst comprising a nickel-basedactive phase and an alumina support, said catalyst comprising between 1%and 50% by weight of elemental nickel relative to the total weight ofthe catalyst, said catalyst being characterized in that:

-   -   the nickel is distributed both on a crust at the periphery of        the support, and in the core of the support, the thickness of        said crust being between 2% and 15% of the diameter of the        catalyst;    -   the nickel density ratio between the crust and the core is        strictly greater than 3;    -   said crust comprises more than 25% by weight of nickel element        relative to the total weight of nickel contained in the        catalyst,    -   the size of the nickel particles in the catalyst, measured in        oxide form, is between 7 and 25 nm.

Advantageously, the nickel density ratio between the crust and the coreis greater than or equal to 3.5.

Advantageously, said crust comprises more than 40% by weight of nickelelement relative to the total weight of nickel contained in thecatalyst.

Advantageously, the transition interval between the core and the crustof the catalyst is between 0.05% and 3% of the diameter of the catalyst.

Advantageously, the size of the nickel particles in the catalyst isbetween 8 and 23 nm.

Advantageously, the sulfur content of the alumina support is between0.001% and 2% by weight relative to the total weight of the aluminasupport, and the sodium content of said alumina support is between0.001% and 2% by weight relative to the total weight of said aluminagel.

Advantageously, the thickness of said crust is between 2.5% and 12% ofthe diameter of the catalyst.

Advantageously, the nickel density ratio between the crust and the coreis between 3.8 and 15.

Another subject according to the invention relates to a process forpreparing a catalyst according to the invention, which process comprisesthe following steps:

-   -   a) an alumina gel is provided;    -   b) the alumina gel from step a) is shaped;    -   c) the shaped alumina gel obtained at the end of step b) is        subjected to a heat treatment comprising at least one        hydrothermal treatment step in an autoclave in the presence of        an acid solution, at a temperature of between 100° C. and 800°        C., and at least one calcining step, at a temperature of between        400° C. and 1500° C., carried out after the hydrothermal        treatment step, in order to obtain an alumina support;    -   d) the alumina support obtained at the end of step c) is brought        into contact with at least one precursor of the nickel active        phase in order to obtain a catalyst precursor,    -   e) the catalyst precursor obtained at the end of step d) is        dried at a temperature below 250° C.;    -   f) the dried catalyst precursor obtained at the end of step e)        is brought into contact with at least one solution containing at        least one organic additive chosen from aldehydes containing 1 to        14 carbon atoms per molecule, ketones or polyketones containing        3 to 18 carbon atoms per molecule, ethers and esters containing        2 to 14 carbon atoms per molecule, alcohols or polyalcohols        containing 1 to 14 carbon atoms per molecule and carboxylic        acids or polycarboxylic acids containing 1 to 14 carbon atoms        per molecule, the mole ratio between the organic additive and        the nickel being greater than 0.05 mol/mol;    -   g) a hydrothermal treatment of the catalyst precursor obtained        at the end of step f) is carried out at a temperature between        100° C. and 200° C. under a gas stream comprising between 5 and        650 grams of water per kg of dry gas.

Advantageously, the process further comprises a step h) of drying thecatalyst precursor obtained at the end of step g) at a temperaturebetween 50° C. and 200° C. under a gas stream comprising an amount ofwater strictly less than 5 grams of water per kg of dry gas.

Advantageously, the process further comprises a step e1) of calciningthe dried catalyst precursor obtained at the end of step e), under a gasstream comprising an amount of water strictly less than 150 grams ofwater per kg of dry gas at a temperature between 250° C. and 1000° C.

Advantageously, in step f), the organic additive is chosen from formicacid, formaldehyde, acetic acid, citric acid, oxalic acid, glycolicacid, malonic acid, ethanol, methanol, ethyl formate, methyl formate,paraldehyde, acetaldehyde, gamma-valerolactone, glucose and sorbitol,trioxane. Preferably, the organic additive is formic acid.

Another subject according to the invention relates to a process for theselective hydrogenation of polyunsaturated compounds containing at least2 carbon atoms per molecule, contained in a hydrocarbon feedstock havinga final boiling point below or equal to 300° C., said process beingcarried out at a temperature of between 0° C. and 300° C., at a pressureof between 0.1 and 10 MPa, at a hydrogen/(polyunsaturated compounds tobe hydrogenated) mole ratio of between 0.1 and 10 and at an hourly spacevelocity of between 0.1 and 200 h⁻¹ when the process is carried out inthe liquid phase, or at a hydrogen/(polyunsaturated compounds to behydrogenated) mole ratio of between 0.5 and 1000 and at an hourly spacevelocity of between 100 and 40 000 h⁻¹ when the process is carried outin the gas phase, in the presence of a catalyst according to theinvention.

Another subject according to the invention relates to a process for thehydrogenation of at least one aromatic or polyaromatic compoundcontained in a hydrocarbon feedstock having a final boiling point belowor equal to 650° C., said process being carried out in the gas phase orin the liquid phase, at a temperature of between 30° C. and 350° C., ata pressure of between 0.1 and 20 MPa, at a hydrogen/(aromatic compoundsto be hydrogenated) mole ratio of between 0.1 and 10 and at an hourlyspace velocity (HSV) of between 0.05 and 50 h⁻¹, in the presence of acatalyst according to the invention.

DESCRIPTION OF THE FIGURE

FIG. 1 is a diagram showing the distribution of nickel in the catalyst.The x-axis corresponds to the thickness of the catalyst, measured fromthe edge of the catalyst (in μm). The y-axis corresponds to the nickeldensity (in grams of Ni/mm³). The nickel is distributed both on a crustat the periphery of the support, of thickness ep1, and in the core ofthe support. The nickel density on the crust d_(crust) is greater thanthe nickel density in the core of the support d_(core). The transitioninterval between the core and the crust of the catalyst has a thicknessdenoted ep2-ep1.

DETAILED DESCRIPTION OF THE INVENTION 1. Definitions

In the text hereinbelow, the groups of chemical elements are givenaccording to the CAS classification (CRC Handbook of Chemistry andPhysics, published by CRC Press, editor-in-chief D. R. Lide, 81stedition, 2000-2001). For example, group VIII according to the CASclassification corresponds to the metals of columns 8, 9 and 10according to the new IUPAC classification.

In the present description, according to the IUPAC convention,“micropores” are understood to mean pores having a diameter of less than2 nm, i.e. 0.002 μm; “mesopores” are understood to mean pores having adiameter of greater than or equal to 2 nm, i.e. 0.002 μm, and less thanor equal to 50 nm, i.e. 0.05 μm, and “macropores” are understood to meanpores having a diameter of greater than 50 nm, i.e. 0.05 μm.

In order to analyze the distribution of the metallic phase on thesupport, a crust thickness is measured by Castaing microprobe (orelectron microprobe microanalysis). The device used is a CAMECA XS100,equipped with four monochromator crystals allowing the simultaneousanalysis of four elements. The Castaing microprobe analysis techniqueconsists of the detection of X-rays emitted by a solid after excitationof its elements by a high-energy electron beam. For the purposes of thischaracterization, the catalyst grains are coated in blocks of epoxyresin. These blocks are polished until the cross section through thediameter of the beads or extrudates is reached, and then metallized bydepositing carbon in a metal evaporator. The electron probe is scannedalong the diameter of five beads or extrudates to obtain the meandistribution profile of the constituent elements of the solids. Thismethod, well known to those skilled in the art, is defined in thepublication by L. Sorbier et al. “Measurement of palladium crustthickness on catalyst by EPMA”, Materials Science and Engineering 32(2012). It makes it possible to establish the distribution profile of agiven element, here nickel, within the grain. Furthermore, the Niconcentration is defined for each measurement and therefore for eachanalysis step. The density of Ni within the grain is therefore definedas the concentration of Ni per mm³.

The total pore volume is measured by mercury porosimetry according tothe standard ASTM D4284-92 with a wetting angle of 140°, for exampleusing an Autopore III™ model device from the brand Micromeritics™.

The BET specific surface area is measured by nitrogen physisorptionaccording to the standard ASTM D3663-03, a method described in the workby Rouquerol F., Rouquerol J. and Singh K., “Adsorption by Powders &Porous Solids: Principles, Methodology and Applications”, AcademicPress, 1999.

The median mesopore diameter is also defined as being the diameter suchthat all the pores, among the combined pores constituting the mesoporevolume, with a size of less than this diameter constitute 50% of thetotal mesopore volume determined by intrusion with a mercuryporosimeter.

“Size of the nickel particles” is understood to mean the diameter of thenickel crystallites in oxide form. The diameter of the nickelcrystallites in oxide form is determined by X-ray diffraction, from thewidth of the diffraction line located at the angle 2θ=43° (i.e. alongthe crystallographic direction [200]) using the Scherrer relationship.This method, used in X-ray diffraction on polycrystalline samples orpowders, which links the full width at half maximum of the diffractionpeaks to the size of the particles, is described in detail in thereference: Appl. Cryst. (1978), 11, 102-113, “Scherrer after sixtyyears: A survey and some new results in the determination of crystallitesize”, J. I. Langford and A. J. C. Wilson.

The content of nickel is measured by X-ray fluorescence.

2. Catalyst

The invention relates to a catalyst comprising, preferably consistingof, a nickel-based active phase, and an alumina support advantageouslycontaining sulfur and sodium, said catalyst comprising between 1% and50% by weight of elemental nickel relative to the total weight of thecatalyst, said catalyst being characterized in that:

-   -   the nickel is distributed both on a crust at the periphery of        the support, and in the core of the support, the thickness of        said crust (also referred to as ep1) being between 2% and 15% of        the diameter of the catalyst, preferably between 2.5% and 12% of        the diameter of the catalyst, even more preferably between 3%        and 10% of the diameter of the catalyst and even more preferably        between 3% and 7.5% of the diameter of the catalyst;    -   the nickel density ratio between the crust and the core (also        referred to here as d_(crust)/d_(core)) is strictly greater than        3, preferably greater than 3.5 and preferably between 3.8 and        15;    -   said crust comprises more than 25% by weight of nickel element        relative to the total weight of nickel element contained in the        catalyst, preferably more than 40% by weight, more        preferentially between 45% and 90% by weight, and even more        preferably between 60% and 90% by weight.

Advantageously, the transition interval between the core and the crustof the catalyst (also referred to here as the core/crust transitioninterval, or ep2-ep1 according to the notations in FIG. 1), linked tothe variation in the nickel density measured over the thickness of thecatalyst from the edge of the catalyst to the center of the catalyst, isvery abrupt. Preferably, the core/crust transition interval is between0.05% and 3% of the diameter of the catalyst, preferably between 0.5%and 2.5% of the diameter of the catalyst.

The nickel content in said catalyst according to the invention isadvantageously between 1% and 50% by weight relative to the total weightof the catalyst, more preferentially between 2% and 40% by weight andeven more preferentially between 3% and 35% by weight and even morepreferentially 5% and 25% by weight relative to the total weight of thecatalyst. The “% by weight” values are based on the elemental form ofnickel.

The catalyst according to the invention can be described as a “semieggshell” catalyst in which the concentration of nickel is higher at theperiphery of the support than in the core of the support, saidconcentration of nickel in the core of the support being non-zero.

The specific surface area of the catalyst is generally between 10 m²/gand 200 m²/g, preferably between 25 m²/g and 110 m²/g, more preferablybetween 40 m²/g and 100 m²/g.

The total pore volume of the catalyst is generally between 0.1 and 1ml/g, preferably between 0.2 ml/g and 0.8 ml/g, and particularlypreferably between 0.3 ml/g and 0.7 ml/g.

The size of the nickel particles, measured in oxide form, in thecatalyst is between 7 and 25 nm, preferably between 8 and 23 nm.

The active phase of the catalyst does not comprise a metal from GroupVIB. In particular, it does not comprise molybdenum or tungsten.

Said catalyst (and the support used for the preparation of the catalyst)is in the form of grains advantageously having a diameter of between 0.5and 10 mm. The grains may have any form known to those skilled in theart, for example the form of beads (preferably having a diameter ofbetween 1 and 8 mm), of extrudates, of tablets or of hollow cylinders.Preferably, the catalyst (and the support used for the preparation ofthe catalyst) are in the form of extrudates with a diameter of between0.5 and 10 mm, preferably between 0.8 and 3.2 mm and very preferablybetween 1.0 and 2.5 mm and with a length of between 0.5 and 20 mm. The“diameter” of the extrudates is intended to mean the diameter of thecircle circumscribed in the cross section of these extrudates. Thecatalyst can advantageously be presented in the form of cylindrical,multilobate, trilobate or quadrilobate extrudates. Preferably, its shapewill be trilobate or quadrilobate. The shape of the lobes could beadjusted according to all the methods known from the prior art.

3. Support

The characteristics of the alumina, mentioned in this section,correspond to the characteristics of the alumina before impregnation ofthe nickel active phase, i.e. the alumina support obtained at the end ofstep c) of the process for preparing the catalyst according to theinvention.

According to the invention, the support is an alumina, that is to saythat the support comprises at least 95%, preferably at least 98%, andparticularly preferably at least 99% by weight of alumina relative tothe weight of the support. The alumina generally has a crystallographicstructure of delta, gamma or theta alumina type, alone or as a mixture.

According to the invention, the alumina support may comprise impuritiessuch as oxides of metals from groups IIA, IIIB, IVB, IIB, IIIA, IVAaccording to the CAS classification, preferably silica, titaniumdioxide, zirconium dioxide, zinc oxide, magnesium oxide and calciumoxide, or else alkali metals, preferably lithium, sodium or potassium,and/or alkaline-earth metals, preferably magnesium, calcium, strontiumor barium or else sulfur.

Advantageously, the sulfur content of the alumina support is between0.001% and 2% by weight relative to the total weight of the aluminasupport, and the sodium content of said alumina support is between0.001% and 2% by weight relative to the total weight of said aluminagel.

The specific surface area of the alumina is generally between 10 m²/gand 250 m²/g, preferably between 30 m²/g and 200 m²/g, more preferablybetween 50 m²/g and 150 m²/g.

The pore volume of the alumina is generally between 0.1 ml/g and 1.2ml/g, preferably between 0.3 ml/g and 0.9 ml/g, and very preferablybetween 0.5 ml/g and 0.9 ml/g.

Process for Preparing the Catalyst

Another subject according to the invention relates to a process forpreparing a catalyst according to the invention, comprising at least thefollowing steps:

-   -   a) an alumina gel is provided, advantageously having a sulfur        content of between 0.001% and 2% by weight relative to the total        weight of said alumina gel, and a sodium content of between        0.001% and 2% by weight relative to the total weight of said        alumina gel;    -   b) the alumina gel from step a) is shaped;    -   c) the shaped alumina gel obtained at the end of step b) is        subjected to a heat treatment comprising at least one        hydrothermal treatment step in an autoclave in the presence of        an acid solution, at a temperature of between 100° C. and 800°        C., and at least one calcining step, at a temperature of between        400° C. and 1500° C., carried out after the hydrothermal        treatment step, in order to obtain an alumina support;    -   d) the alumina support obtained at the end of step c) is brought        into contact with at least one precursor of the nickel active        phase in order to obtain a catalyst precursor;    -   e) the catalyst precursor obtained at the end of step d) is        dried at a temperature below 250° C.;    -   e1) optionally, a heat treatment of the dried catalyst precursor        obtained at the end of step e) is carried out at a temperature        of between 250° C. and 1000° C. in order to obtain a calcined        catalyst precursor;    -   f) the dried catalyst precursor obtained at the end of step e),        optionally the calcined catalyst precursor obtained at the end        of step e1), is brought into contact with at least one solution        containing at least one organic additive chosen from aldehydes        containing from 1 to 14 carbon atoms per molecule, ketones or        polyketones containing from 3 to 18 carbon atoms per molecule,        ethers or esters containing from 2 to 14 carbon atoms per        molecule, alcohols or polyalcohols containing from 1 to 14        carbon atoms per molecule and carboxylic acids or polycarboxylic        acids containing from 1 to 14 carbon atoms per molecule, the        mole ratio between the organic additive and the nickel being        greater than 0.05 mol/mol;    -   g) a hydrothermal treatment of the catalyst precursor obtained        at the end of step f) is carried out at a temperature between        100° C. and 200° C. for a period of between 30 minutes and 5        hours under a gas stream comprising between 5 and 650 grams of        water per kilogram of dry gas;    -   h) optionally, a step of drying the catalyst precursor obtained        at the end of step g) between 50° C. and 200° C. is carried out        under a gas stream comprising an amount of water strictly less        than 5 grams of water per kilogram of dry gas.

The order of the steps from a) to h) cannot be changed. However,intermediate steps can be inserted (in particular additional dryingsteps) and certain steps can be carried out several times in a row (forexample step d)). Finally, it is possible to add additional steps beforeusing the catalyst at the end of step h).

Preferably, a step of drying and then a step of calcining is carried outat the end of the shaping step b) (but before carrying out step c).

Preferably, steps e1) and h) are not optional.

Steps a) to h) of said preparation process are described in detailbelow.

Step a)

The catalyst according to the invention comprises an alumina supportwhich is obtained from an alumina gel which essentially comprises aprecursor of aluminum oxy(hydroxide) (AlO(OH)) type—also known asboehmite.

According to the invention, the alumina gel (or otherwise known asboehmite gel) is synthesized by precipitation of basic and/or acidicsolutions of aluminum salts induced by a change in pH or any othermethod known to those skilled in the art (P. Euzen, P. Raybaud, X.Krokidis, H. Toulhoat, J. L. Le Loarer, J. P. Jolivet and C. Froidefond,Alumina, in “Handbook of Porous Solids”, edited by F. Schüth, K. S. W.Sing and J. Weitkamp, Wiley-VCH, Weinheim, Germany, 2002, pp.1591-1677).

Generally the precipitation reaction is carried out at a temperature ofbetween 5° C. and 80° C., and at a pH of between 6 and 10. Preferably,the temperature is between 35° C. and 70° C. and the pH is between 6 and10.

According to one embodiment, the alumina gel is obtained by bringing anaqueous solution of an acid salt of aluminum into contact with a basicsolution. For example, the acid salt of aluminum is chosen from thegroup consisting of aluminum sulfate, aluminum nitrate or aluminumchloride and preferably said acid salt is aluminum sulfate. The basicsolution is preferentially chosen from sodium hydroxide or potassiumhydroxide.

Alternatively, an alkaline solution of aluminum salts which may bechosen from the group consisting of sodium aluminate and potassiumaluminate may be brought into contact with an acid solution. In a verypreferred variant, the gel is obtained by bringing a sodium aluminatesolution into contact with nitric acid. The sodium aluminate solutionadvantageously has a concentration of between 10⁻⁵ and 10⁻¹ mol.L⁻¹ andpreferably this concentration is between 10⁻⁴ and 10⁻² mol.L⁻¹.

According to another embodiment, the alumina gel is obtained by bringingan aqueous solution of acid salts of aluminum into contact with analkaline solution of aluminum salts.

Step b)

The support may advantageously be shaped by any technique known to thoseskilled in the art. The shaping may be carried out for example bykneading-extrusion, by pelletizing, by the drop coagulation (oil-drop)method, by granulation on a rotating plate or by any other method thatis well known to those skilled in the art. The catalysts according tothe invention can optionally be manufactured and used in the form ofextrudates, tablets, beads. The advantageous shaping method according tothe invention is extrusion and the preferred extrudate shapes arecylindrical, twisted cylindrical or multilobate (2, 3, 4 or 5 lobes forexample).

In a particular embodiment, the alumina gel obtained at the end of stepa) is subjected to a step of kneading, preferably in an acidic medium.The acid used may for example be nitric acid. This step is carried outby means of known tools such as Z-arm mixers, grinding mixers,continuous single or twin screws that enable the gel to be convertedinto a product having the consistency of a paste. According to oneadvantageous embodiment, one or more compounds referred to as“pore-forming agents” are introduced into the kneading medium. Thesecompounds have the property of degrading on heating and thus creatingporosity in the support. For example, wood flour, charcoal, tars andplastics can be used as pore-forming compounds. The paste thus obtainedafter kneading is passed through an extrusion die. Generally theextrudates have a diameter of between 0.5 and 10 mm, preferably between0.8 and 3.2 mm and very preferably between 1.0 and 2.5 mm and a lengthof between 0.5 and 20 mm. These extrudates can be cylindrical,multilobate (for example trilobate or quadrilobate).

After the shaping thereof, the support is optionally dried beforeundergoing the hydrothermal treatment according to step c) of theprocess. For example, the drying is carried out at a temperature between50° C. and 200° C. The dried support is optionally calcined beforeundergoing the hydrothermal treatment according to step c) of theprocess. For example, the calcining is carried out at a temperaturebetween 200° C. and 1000° C., in the presence or absence of a stream ofair containing up to 150 grams of water per kilogram of dry air.

Step c)

The support obtained at the end of step b) then undergoes a heattreatment step which makes it possible to give it physical propertiesthat satisfy the envisaged application.

The term “hydrothermal treatment” denotes a treatment by passing throughan autoclave in the presence of water at a temperature above roomtemperature.

During this hydrothermal treatment, the shaped alumina can be treated indifferent ways. Thus, the alumina can be impregnated with an acidsolution, prior to passing through the autoclave, it being possible forthe hydrothermal treatment of the alumina to be carried out either inthe vapor phase or in the liquid phase, it being possible for this vaporor liquid phase of the autoclave to be acidic or non-acidic. Thisimpregnation, prior to the hydrothermal treatment, may be performed dryor by immersing the alumina in an acidic aqueous solution. The term “dryimpregnation” means placing the alumina in contact with a volume ofsolution less than or equal to the total pore volume of the treatedalumina. Preferably, the impregnation is performed dry.

It is also possible to treat the extruded support without priorimpregnation with an acidic solution, the acidity in this case beingprovided by the aqueous liquid of the autoclave.

The acidic aqueous solution comprises at least one acidic compound fordissolving at least one portion of the alumina of the extrudates. Theterm “acidic compound for dissolving at least one portion of the aluminaof the extrudates” is understood to mean any acidic compound which,brought into contact with the alumina extrudates, dissolves at least oneportion of the aluminum ions. The acid should preferably dissolve atleast 0.5% by weight of alumina of the alumina extrudates.

Preferably, this acid is chosen from strong acids such as nitric acid,hydrochloric acid, perchloric acid, sulfuric acid or a weak acid used ata concentration such that its aqueous solution has a pH of less than 4,such as acetic acid, or a mixture of these acids.

According to a preferred embodiment, the hydrothermal treatment iscarried out in the presence of nitric acid and acetic acid taken aloneor as a mixture. The autoclave is preferably a rotating basketautoclave, such as the one defined in patent application EP-A-0 387 109.

The hydrothermal treatment may also be carried out under saturationvapor pressure or under a partial pressure of water vapor at least equalto 70% of the saturation vapor pressure corresponding to the treatmenttemperature.

Preferably the hydrothermal treatment is conducted at a temperature ofbetween 100° C. and 800° C., preferably between 200° C. and 700° C. Thehydrothermal treatment is generally carried out for between 30 minutesand 8 hours, preferably between 30 minutes and 3 hours. Preferably, thecalcining step which takes place after the hydrothermal treatment in theautoclave takes place at a temperature generally of between 400° C. and1500° C., preferably between 800° C. and 1300° C., generally for 1 and 5hours, in air, the water content of which is generally between 0 and 700g of water per kilogram of dry air.

At the end of step c), the alumina obtained exhibits the specifictextural properties as described above.

Step d)

The support may be brought into contact with a solution containing anickel precursor, in accordance with the implementation of step d), bydry impregnation or excess impregnation, or else bydeposition-precipitation, according to methods well known to thoseskilled in the art.

Said step d) is preferentially carried out by impregnation of thesupport consisting, for example, of bringing the support into contactwith at least one aqueous solution containing a nickel precursor. The pHof said solution could be modified by the optional addition of an acidor of a base.

Preferably, said step d) is carried out by dry impregnation, whichconsists in bringing the support into contact with at least one solutioncontaining, preferably consisting of, at least one nickel precursor, thevolume of the solution of which is between 0.25 and 1.5 times the porevolume of the support to be impregnated.

Preferably, said nickel precursor is introduced in aqueous solution, forexample in nitrate, carbonate, acetate, chloride or oxalate form, in theform of complexes formed by a polyacid or an acid alcohol and its salts,in the form of complexes formed with acetylacetonates or in the form ofany other inorganic derivative soluble in aqueous solution, which isbrought into contact with said support. Preferably, use isadvantageously made, as nickel precursor, of nickel nitrate, nickelchloride, nickel acetate or nickel hydroxycarbonate. Very preferably,the nickel precursor is nickel nitrate.

According to another variant, the aqueous solution may contain aqueousammonia or ammonium NH₄+ ions.

The concentration of nickel in solution is adjusted depending on thetype of impregnation (dry impregnation or excess impregnation) and thepore volume of the support so as to obtain, for the supported catalyst,a nickel content of between 1% and 50% by weight of nickel elementrelative to the total weight of the catalyst, more preferentiallybetween 2% and 40% by weight and even more preferentially between 3% and35% by weight and even more preferentially 5% and 25% by weight.

Step e)

The drying step is carried out under a gas stream comprising an amountof water of less than 150 grams of water per kilogram of dry gas,preferably less than 50 g of water per kilogram of dry gas, at atemperature below 250° C., preferably between 15° C. and 240° C., morepreferentially between 30° C. and 220° C., more preferentially stillbetween 50° C. and 200° C., and even more preferentially between 70° C.and 180° C., generally for a period of between 10 minutes and 24 hours.Longer periods of time are not ruled out, but do not necessarily provideany improvement.

The gas may contain oxygen, nitrogen or an inert gas and preferably thegas is air.

Optional Step e1)

The optional calcining step is carried out under a gas stream comprisingan amount of water of less than 150 grams of water per kilogram of drygas, preferably less than 50 g of water per kilogram of dry gas, at atemperature of between 250° C. and 1000° C., preferably between 250° C.and 750° C. The duration of this heat treatment is generally between 15minutes and 10 hours. Longer periods of time are not ruled out, but donot necessarily provide any improvement.

The gas may contain oxygen, nitrogen or an inert gas and preferably thegas is air.

At the end of steps e) or e1), the nickel is distributed homogeneouslyon the support.

Step f)

According to step f) of the process for preparing the catalyst, thecatalyst precursor obtained at the end of step e), optionally at the endof step e1), is brought into contact with at least one solutioncomprising at least one organic additive chosen from aldehydescontaining from 1 to 14 (preferably from 2 to 12) carbon atoms permolecule, ketones or polyketones containing from 3 to 18 (preferablyfrom 3 to 12) carbon atoms per molecule, ethers or esters containingfrom 2 to 14 (preferably from 3 to 12) carbon atoms per molecule,alcohols or polyalcohols containing from 1 to 14 (preferably from 2 to12) carbon atoms per molecule and carboxylic acids or polycarboxylicacids containing from 1 to 14 (preferably from 1 to 12) carbon atoms permolecule. The organic additive may be composed of a combination of thevarious functional groups mentioned above.

Preferably, the organic additive is chosen from formic acid HCOOH,formaldehyde CH₂O, acetic acid CH₃COOH, citric acid, oxalic acid,glycolic acid (HOOC—CH₂—OH), malonic acid (HOOC—CH₂—COOH), ethanol,methanol, ethyl formate HCOOC₂H₅, methyl formate HCOOCH₃, paraldehyde(CH₃—CHO)₃, acetaldehyde C₂H₄O, gamma-valerolactone (C₅H₈O₂), glucoseand sorbitol, trioxane.

Particularly preferably, the organic additive is formic acid.

It is essential that the step of adding the organic additive to thecatalyst (step f)) is carried out after the step of bringing the supportinto contact with the precursor of the nickel active phase.

Preferably, said step f) is carried out by impregnating the catalystprecursor obtained at the end of the implementation of step e) or ofstep e1) with a solution comprising at least one organic additive asmentioned above. The impregnation is generally carried out in aqueoussolution or in organic solution or in suspension in aqueous or organicsolution, preferably in aqueous solution. When the operation is carriedout in organic solution or suspension, an alcohol or polyalcohol, glycolor polyglycol will preferably be used as organic solvent.

Preferably, said step f) is carried out by dry impregnation, whichconsists in bringing the catalyst precursor obtained at the end of theimplementation of step e) or of step e1) into contact with a solutioncomprising at least one organic additive as mentioned above, the volumeof the solution of which is between 0.25 and 1.5 times the pore volumeof the catalyst precursor to be impregnated.

The impregnation is generally carried out at a temperature between 0° C.and 50° C., preferably between 10° C. and 40° C., and particularlypreferably at room temperature.

According to the invention, the mole ratio between the organic additiveand the nickel is greater than 0.05 mol/mol, preferably between 0.1 and5 mol/mol, more preferentially between 0.12 and 3 mol/mol, and even morepreferably between 0.15 and 2.5 mol/mol.

Step g)

According to step g) of the process for preparing the catalyst accordingto the invention, a hydrothermal treatment of the product resulting fromstep f) is carried out at a temperature of between 100° C. and 200° C.,preferably between 130° C. and 170° C., and more particularly around150° C., under a gas stream comprising between 5 and 650 grams of waterper kilogram of dry gas, preferably between 7 and 150 grams of water perkilogram of dry gas, even more preferably between 10 and 50 grams ofwater per kilogram of dry gas. The gas may contain oxygen, nitrogen oran inert gas and preferably the gas is air.

The duration of the hydrothermal treatment is generally between 30minutes and 5 hours, preferably between 1 to 3 hours.

Step h) (Optional)

Step g) can be followed by a step h) of drying between 50° C. and 200°C. under a gas stream comprising an amount of water strictly less than 5grams of water per kilogram of dry gas, advantageously for a time ofbetween 30 minutes and 5 hours, preferably between 1 to 3 hours.

The gas may contain oxygen, nitrogen or an inert gas and preferably thegas is air.

At the end of step g), or optionally of step h), a “semi eggshell”catalyst is obtained as shown schematically in FIG. 1 and thecharacteristics of which are described above.

Step i) (Optional)

Prior to the use of the catalyst in the catalytic reactor and theimplementation of a hydrogenation process, at least one reducingtreatment step i) is advantageously carried out in the presence of areducing gas after steps g) or h) so as to obtain a catalyst comprisingnickel at least partially in the metallic form.

This treatment makes it possible to activate said catalyst and to formmetal particles, in particular of nickel in the zero-valent state. Saidreducing treatment may be carried out in situ or ex situ, i.e. after orbefore the charging of the catalyst to the hydrogenation reactor.

The reducing gas is preferably hydrogen. The hydrogen can be used pureor as a mixture (for example a hydrogen/nitrogen, or hydrogen/argon, orhydrogen/methane mixture). In the case where the hydrogen is used as amixture, all proportions can be envisaged.

Said reducing treatment is carried out at a temperature between 120° C.and 500° C., preferably between 150° C. and 450° C. When the catalystdoes not undergo passivation, or undergoes a reducing treatment beforepassivation, the reducing treatment is carried out at a temperaturebetween 180° C. and 500° C., preferably between 200° C. and 450° C., andmore preferentially between 350° C. and 450° C. When the catalyst hasundergone a passivation beforehand, the reducing treatment is generallycarried out at a temperature between 120° C. and 350° C., preferablybetween 150° C. and 350° C.

The duration of the reducing treatment is generally between 2 and 40hours, preferably between 3 and 30 hours. The rise in temperature up tothe desired reduction temperature is generally slow, for example setbetween 0.1 and 10° C./min, preferably between 0.3 and 7° C./min.

The hydrogen flow rate, expressed in l/hour/gram of catalyst, is between0.01 and 100 l/hour/gram of catalyst, preferably between 0.05 and 10l/hour/gram of catalyst and more preferably still between 0.1 and 5l/hour/gram of catalyst.

Selective Hydrogenation Process

Another subject of the present invention is a process for the selectivehydrogenation of polyunsaturated compounds containing at least 2 carbonatoms per molecule, such as diolefins and/or acetylenics and/oralkenylaromatics, also known as styrenics, contained in a hydrocarbonfeedstock having a final boiling point below or equal to 300° C., saidprocess being carried out at a temperature of between 0° C. and 300° C.,at a pressure of between 0.1 and 10 MPa, at a hydrogen/(polyunsaturatedcompounds to be hydrogenated) mole ratio of between 0.1 and 10 and at anhourly space velocity of between 0.1 and 200 h⁻¹ when the process iscarried out in the liquid phase, or at a hydrogen/(polyunsaturatedcompounds to be hydrogenated) mole ratio of between 0.5 and 1000 and atan hourly space velocity of between 100 and 40 000 h⁻¹ when the processis carried out in the gas phase, in the presence of a catalyst obtainedby the preparation process as described above in the description.

Monounsaturated organic compounds, such as, for example, ethylene andpropylene, are at the root of the manufacture of polymers, of plasticsand of other chemicals having added value. These compounds are obtainedfrom natural gas, from naphtha or from gas oil which have been treatedby steam cracking or catalytic cracking processes. These processes arecarried out at high temperature and produce, in addition to the desiredmonounsaturated compounds, polyunsaturated organic compounds, such asacetylene, propadiene and methylacetylene (or propyne), 1,2-butadieneand 1,3-butadiene, vinylacetylene and ethylacetylene, and otherpolyunsaturated compounds, the boiling point of which corresponds to theC5+ fraction (hydrocarbon-based compounds having at least 5 carbonatoms), in particular diolefinic or styrene or indene compounds. Thesepolyunsaturated compounds are highly reactive and result in sidereactions in the polymerization units. It is thus necessary to removethem before making economic use of these fractions.

Selective hydrogenation is the main treatment developed to specificallyremove undesirable polyunsaturated compounds from these hydrocarbonfeedstocks. It makes possible the conversion of polyunsaturatedcompounds to the corresponding alkenes or aromatics while avoiding theircomplete saturation and thus the formation of the corresponding alkanesor naphthenes. In the case of steam cracking gasolines used asfeedstock, the selective hydrogenation also makes it possible toselectively hydrogenate the alkenylaromatics to give aromatics whileavoiding the hydrogenation of the aromatic rings.

The hydrocarbon feedstock treated in the selective hydrogenation processhas a final boiling point of below or equal to 300° C. and contains atleast 2 carbon atoms per molecule and comprises at least onepolyunsaturated compound. The term “polyunsaturated compounds” isintended to mean compounds comprising at least one acetylenic functionand/or at least one diene function and/or at least one alkenylaromaticfunction.

More particularly, the feedstock is selected from the group consistingof a steam cracking C2 fraction, a steam cracking C2-C3 fraction, asteam cracking C3 fraction, a steam cracking C4 fraction, a steamcracking C5 fraction and a steam cracking gasoline, also known aspyrolysis gasoline or C5+ fraction.

The steam cracking C2 fraction, advantageously used for theimplementation of the selective hydrogenation process according to theinvention, exhibits, for example, the following composition: between 40%and 95% by weight of ethylene and of the order of 0.1% to 5% by weightof acetylene, the remainder being essentially ethane and methane. Insome steam cracking C2 fractions, between 0.1% and 1% by weight of C3compounds may also be present.

The steam cracking C3 fraction, advantageously used for theimplementation of the selective hydrogenation process according to theinvention, exhibits, for example, the following mean composition: of theorder of 90% by weight of propylene and of the order of 1% to 8% byweight of propadiene and of methylacetylene, the remainder beingessentially propane. In some C3 fractions, between 0.1% and 2% by weightof C2 compounds and of C4 compounds may also be present.

A C2-C3 fraction can also advantageously be used for the implementationof the selective hydrogenation process according to the invention. Itexhibits, for example, the following composition: of the order of 0.1%to 5% by weight of acetylene, of the order of 0.1% to 3% by weight ofpropadiene and of methylacetylene, of the order of 30% by weight ofethylene and of the order of 5% by weight of propylene, the remainderbeing essentially methane, ethane and propane. This feedstock may alsocontain between 0.1% and 2% by weight of C4 compounds.

The steam cracking C4 fraction, advantageously used for theimplementation of the selective hydrogenation process according to theinvention, exhibits, for example, the following mean composition byweight: 1% by weight of butane, 46.5% by weight of butene, 51% by weightof butadiene, 1.3% by weight of vinylacetylene and 0.2% by weight ofbutyne. In some C4 fractions, between 0.1% and 2% by weight of C3compounds and of C5 compounds may also be present.

The steam cracking C5 fraction, advantageously used for theimplementation of the selective hydrogenation process according to theinvention, exhibits, for example, the following composition: 21% byweight of pentanes, 45% by weight of pentenes and 34% by weight ofpentadienes.

The steam cracking gasoline or pyrolysis gasoline, advantageously usedfor the implementation of the selective hydrogenation process accordingto the invention, corresponds to a hydrocarbon fraction, the boilingpoint of which is generally between 0 and 300° C., preferably between 10and 250° C. The polyunsaturated hydrocarbons to be hydrogenated presentin said steam cracking gasoline are in particular diolefin compounds(butadiene, isoprene, cyclopentadiene, and the like), styrene compounds(styrene, α-methylstyrene, and the like) and indene compounds (indene,and the like). The steam cracking gasoline generally comprises theC5-C12 fraction with traces of C3, C4, C13, C14 and C15 (for examplebetween 0.1% and 3% by weight for each of these fractions). For example,a feedstock formed of pyrolysis gasoline generally has a composition asfollows: 5% to 30% by weight of saturated compounds (paraffins andnaphthenes), 40% to 80% by weight of aromatic compounds, 5% to 20% byweight of mono-olefins, 5% to 40% by weight of diolefins and 1% to 20%by weight of alkenylaromatic compounds, the combined compounds forming100%. It also contains from 0 to 1000 ppm by weight of sulfur,preferably from 0 to 500 ppm by weight of sulfur.

Preferably, the polyunsaturated hydrocarbon feedstock treated inaccordance with the selective hydrogenation process according to theinvention is a steam cracking C2 fraction or a steam cracking C2-C3fraction or a steam cracking gasoline.

The selective hydrogenation process according to the invention istargeted at removing said polyunsaturated hydrocarbons present in saidfeedstock to be hydrogenated without hydrogenating the monounsaturatedhydrocarbons. For example, when said feedstock is a C2 fraction, theselective hydrogenation process is targeted at selectively hydrogenatingacetylene. When said feedstock is a C3 fraction, the selectivehydrogenation process is targeted at selectively hydrogenatingpropadiene and methylacetylene. In the case of a C4 fraction, the aim isto remove butadiene, vinylacetylene (VAC) and butyne; in the case of aC5 fraction, the aim is to remove the pentadienes. When said feedstockis a steam cracking gasoline, the selective hydrogenation process istargeted at selectively hydrogenating said polyunsaturated hydrocarbonspresent in said feedstock to be treated so that the diolefin compoundsare partially hydrogenated to give mono-olefins and so that the styreneand indene compounds are partially hydrogenated to give correspondingaromatic compounds while avoiding the hydrogenation of the aromaticrings.

The technological implementation of the selective hydrogenation processis, for example, carried out by injection, as upflow or downflow, of thepolyunsaturated hydrocarbon feedstock and of the hydrogen into at leastone fixed bed reactor. Said reactor may be of isothermal type or ofadiabatic type. An adiabatic reactor is preferred. The polyunsaturatedhydrocarbon feedstock can advantageously be diluted by one or morereinjection(s) of the effluent, resulting from said reactor where theselective hydrogenation reaction takes place, at various points of thereactor, located between the inlet and the outlet of the reactor, inorder to limit the temperature gradient in the reactor. Thetechnological implementation of the selective hydrogenation processaccording to the invention can also advantageously be carried out by theimplantation of at least said supported catalyst in a reactivedistillation column or in reactors-exchangers or in a slurry-typereactor. The stream of hydrogen may be introduced at the same time asthe feedstock to be hydrogenated and/or at one or more different pointsof the reactor.

The selective hydrogenation of the steam cracking C2, C2-C3, C3, C4, C5and C5+ fractions can be carried out in the gas phase or in the liquidphase, preferably in the liquid phase for the C3, C4, C5 and C5+fractions and in the gas phase for the C2 and C2-C3 fractions. Aliquid-phase reaction makes it possible to lower the energy cost and toincrease the cycle period of the catalyst.

Generally, the selective hydrogenation of a hydrocarbon feedstockcontaining polyunsaturated compounds containing at least 2 carbon atomsper molecule and having a final boiling point below or equal to 300° C.is carried out at a temperature of between 0° C. and 300° C., at apressure of between 0.1 and 10 MPa, at a hydrogen/(polyunsaturatedcompounds to be hydrogenated) mole ratio of between 0.1 and 10 and at anhourly space velocity (defined as the ratio of the flow rate by volumeof feedstock to the volume of the catalyst) of between 0.1 and 200 h⁻¹for a process carried out in the liquid phase, or at ahydrogen/(polyunsaturated compounds to be hydrogenated) mole ratio ofbetween 0.5 and 1000 and at an hourly space velocity of between 100 and40 000 h⁻¹ for a process carried out in the gas phase.

In one embodiment according to the invention, when a selectivehydrogenation process is carried out wherein the feedstock is a steamcracking gasoline comprising polyunsaturated compounds, the(hydrogen)/(polyunsaturated compounds to be hydrogenated) mole ratio isgenerally between 0.5 and 10, preferably between 0.7 and 5.0 and morepreferably still between 1.0 and 2.0, the temperature is between 0° C.and 200° C., preferably between 20° C. and 200° C. and more preferablystill between 30° C. and 180° C., the hourly space velocity (HSV) isgenerally between 0.5 and 100 h⁻¹, preferably between 1 and 50 h⁻¹, andthe pressure is generally between 0.3 and 8.0 MPa, preferably between1.0 and 7.0 MPa and more preferably still between 1.5 and 4.0 MPa.

More preferentially, a selective hydrogenation process is carried outwherein the feedstock is a steam cracking gasoline comprisingpolyunsaturated compounds, the hydrogen/(polyunsaturated compounds to behydrogenated) mole ratio is between 0.7 and 5.0, the temperature isbetween 20° C. and 200° C., the hourly space velocity (HSV) is generallybetween 1 and 50 h⁻¹ and the pressure is between 1.0 and 7.0 MPa.

More preferentially still, a selective hydrogenation process is carriedout wherein the feedstock is a steam cracking gasoline comprisingpolyunsaturated compounds, the hydrogen/(polyunsaturated compounds to behydrogenated) mole ratio is between 1.0 and 2.0, the temperature isbetween 30° C. and 180° C., the hourly space velocity (HSV) is generallybetween 1 and 50 h⁻¹ and the pressure is between 1.5 and 4.0 MPa.

The hydrogen flow rate is adjusted in order to have available asufficient amount thereof to theoretically hydrogenate all of thepolyunsaturated compounds and to maintain an excess of hydrogen at thereactor outlet.

In another embodiment according to the invention, when a selectivehydrogenation process is carried out wherein the feedstock is a steamcracking C2 fraction and/or a steam cracking C2-C3 fraction comprisingpolyunsaturated compounds, the (hydrogen)/(polyunsaturated compounds tobe hydrogenated) mole ratio is generally between 0.5 and 1000,preferably between 0.7 and 800, the temperature is between 0° C. and300° C., preferably between 15° C. and 280° C., the hourly spacevelocity (HSV) is generally between 100 and 40 000 h⁻¹, preferablybetween 500 and 30 000 h⁻¹, and the pressure is generally between 0.1and 6.0 MPa, preferably between 0.2 and 5.0 MPa.

Aromatics Hydrogenation Process

Another subject of the present invention is a process for thehydrogenation of at least one aromatic or polyaromatic compoundcontained in a hydrocarbon feedstock having a final boiling point belowor equal to 650° C., generally between 20° C. and 650° C., andpreferably between 20° C. and 450° C. Said hydrocarbon feedstockcontaining at least one aromatic or polyaromatic compound can be chosenfrom the following petroleum or petrochemical fractions: the reformatefrom catalytic reforming, kerosene, light gas oil, heavy gas oil,cracking distillates, such as FCC recycle oil, coking unit gas oil orhydrocracking distillates.

The content of aromatic or polyaromatic compounds contained in thehydrocarbon feedstock treated in the hydrogenation process according tothe invention is generally between 0.1 and 80% by weight, preferablybetween 1 and 50% by weight, and particularly preferably between 2 and35% by weight, the percentage being based on the total weight of thehydrocarbon feedstock. The aromatic compounds present in saidhydrocarbon feedstock are, for example, benzene or alkylaromatics, suchas toluene, ethylbenzene, o-xylene, m-xylene or p-xylene, or alsoaromatics having several aromatic rings (polyaromatics), such asnaphthalene.

The sulfur or chlorine content of the feedstock is generally less than5000 ppm by weight of sulfur or chlorine, preferably less than 100 ppmby weight, and particularly preferably less than 10 ppm by weight.

The technological implementation of the process for the hydrogenation ofaromatic or polyaromatic compounds is, for example, carried out byinjection, as upflow or downflow, of the hydrocarbon feedstock and ofthe hydrogen into at least one fixed bed reactor. Said reactor may be ofisothermal type or of adiabatic type. An adiabatic reactor is preferred.The hydrocarbon feedstock may advantageously be diluted by one or morereinjection(s) of the effluent, resulting from said reactor where thereaction for the hydrogenation of the aromatics takes place, at variouspoints of the reactor, located between the inlet and the outlet of thereactor, in order to limit the temperature gradient in the reactor. Thetechnological implementation of the process for the hydrogenation of thearomatics according to the invention may also advantageously be carriedout by the implantation of at least said supported catalyst in areactive distillation column or in reactors-exchangers or in aslurry-type reactor. The stream of hydrogen may be introduced at thesame time as the feedstock to be hydrogenated and/or at one or moredifferent points of the reactor.

The hydrogenation of the aromatic or polyaromatic compounds may becarried out in the gas phase or in the liquid phase, preferably in theliquid phase. Generally, the hydrogenation of the aromatic orpolyaromatic compounds is carried out at a temperature of between 30° C.and 350° C., preferably between 50° C. and 325° C., at a pressure ofbetween 0.1 and 20 MPa, preferably between 0.5 and 10 MPa, at ahydrogen/(aromatic compounds to be hydrogenated) mole ratio between 0.1and 10 and at an hourly space velocity of between 0.05 and 50 h⁻¹,preferably between 0.1 and 10 h⁻¹, of a hydrocarbon feedstock containingaromatic or polyaromatic compounds and having a final boiling pointbelow or equal to 650° C., generally between 20° C. and 650° C., andpreferably between 20° C. and 450° C.

The hydrogen flow rate is adjusted in order to have available asufficient amount thereof to theoretically hydrogenate all of thearomatic compounds and to maintain an excess of hydrogen at the reactoroutlet.

The conversion of the aromatic or polyaromatic compounds is generallygreater than 20 mol %, preferably greater than 40 mol %, more preferablygreater than 80 mol %, and particularly preferably greater than 90 mol %of the aromatic or polyaromatic compounds contained in the hydrocarbonfeedstock. The conversion is calculated by dividing the differencebetween the total moles of the aromatic or polyaromatic compounds in thehydrocarbon feedstock and in the product by the total moles of thearomatic or polyaromatic compounds in the hydrocarbon feedstock.

According to a specific alternative form of the process according to theinvention, a process for the hydrogenation of the benzene of ahydrocarbon feedstock, such as the reformate resulting from a catalyticreforming unit, is carried out. The benzene content in said hydrocarbonfeedstock is generally between 0.1 and 40% by weight, preferably between0.5 and 35% by weight, and particularly preferably between 2 and 30% byweight, the percentage by weight being based on the total weight of thehydrocarbon feedstock.

The sulfur or chlorine content of the feedstock is generally less than10 ppm by weight of sulfur or chlorine respectively, and preferably lessthan 2 ppm by weight.

The hydrogenation of the benzene contained in the hydrocarbon feedstockmay be carried out in the gas phase or in the liquid phase, preferablyin the liquid phase. When it is carried out in the liquid phase, asolvent may be present, such as cyclohexane, heptane or octane.Generally, the hydrogenation of the benzene is carried out at atemperature of between 30° C. and 250° C., preferably between 50° C. and200° C., and more preferably between 80° C. and 180° C., at a pressureof between 0.1 and 10 MPa, preferably between 0.5 and 4 MPa, at ahydrogen/(benzene) mole ratio between 0.1 and 10 and at an hourly spacevelocity of between 0.05 and 50 h⁻¹, preferably between 0.5 and 10 h⁻¹.

The conversion of the benzene is generally greater than 50 mol %,preferably greater than 80 mol %, more preferably greater than 90 mol %and particularly preferably greater than 98 mol %.

The invention will now be illustrated by the following examples whichare in no way limiting.

EXAMPLES Example 1 Preparation of the AL-1 Alumina

An alumina gel is synthesized via a mixture of sodium aluminate andaluminum sulfate. The precipitation reaction takes place at atemperature of 60° C., at a pH of 9, for 60 minutes and with stirring at200 rpm.

The gel thus obtained is kneaded in a Z-arm mixer in order to providethe paste. The extrusion is carried out by passing the paste through adie provided with 1.6 mm-diameter orifices of trilobe shape. Theextrudates thus obtained are dried at 150° C. for 12 hours and thencalcined at 450° C. under a stream of dry air for 5 hours. The dry airused in this example and in all the examples below contains less than 5grams of water per kilogram of dry air.

The extrudate undergoes a hydrothermal treatment at 650° C. in thepresence of an aqueous solution containing acetic acid at 6.5% by weightrelative to the weight of alumina for 3 hours in an autoclave, and thenis calcined under a stream of dry air at 1000° C. for 2 hours in atubular reactor. The AL-1 alumina is obtained.

The AL-1 alumina has a specific surface area of 80 m²/g, a pore volume(determined by Hg porosimetry) of 0.85 ml/g and a median mesoporediameter of 35 nm. The sodium content is 0.0350 wt % and the sulfurcontent 0.15 wt %.

Example 1a Preparation of the AL-2 Alumina

An alumina gel is synthesized via a mixture of sodium aluminate andaluminum sulfate. The precipitation reaction takes place at atemperature of 60° C., at a pH of 9, for 60 minutes and with stirring at200 rpm.

The gel thus obtained is kneaded in a Z-arm mixer in order to providethe paste. The extrusion is carried out by passing the paste through adie provided with 1.6 mm-diameter orifices of trilobe shape. Theextrudates thus obtained are dried at 150° C. for 12 hours and thencalcined at 450° C. under a stream of dry air for 5 hours.

The AL-2 alumina is obtained. This alumina does not undergo hydrothermaltreatment.

The AL-2 alumina has a specific surface area of 255 m²/g, a pore volume(determined by Hg porosimetry) of 0.7 ml/g and a median mesoporediameter of 12 nm. The sodium content is 0.0350 wt % and the sulfurcontent 0.15 wt %.

Example 2 Preparation of an Aqueous Solution of Ni Precursors

The aqueous solution of Ni precursors (solution S) used for thepreparation of the catalysts A, C, D, E and F is prepared by dissolving43.5 grams (g) of nickel nitrate (NiNO₃, supplier Strem Chemicals®) in avolume of 13 ml of distilled water. The solution S, the Ni concentrationof which is 350 g of Ni per liter of solution, is obtained.

Example 2a Preparation of a Second Aqueous Solution of Ni Precursors

The aqueous solution of Ni precursors (solution S′) used for thepreparation of the catalyst B is prepared by dissolving 14.5 grams (g)of nickel nitrate (NiNO₃, supplier Strem Chemicals®) in a volume of 13ml of distilled water. The solution S′, the Ni concentration of which isabout 116 g of Ni per liter of solution, is obtained.

Example 3 Preparation of a Catalyst A According to the Invention [15% ByWeight of Ni-organic Additive:Formic Acid]

The solution S prepared in example 2 is dry impregnated, by adding itdropwise, on 10 g of AL-1 alumina obtained according to example 1.

The solid thus obtained is subsequently dried in an oven at 120° C. for12 hours and then calcined under a stream of dry air of 1 l/h/g ofcatalyst at 450° C. for 2 hours.

The catalyst precursor thus obtained is dry impregnated with an aqueoussolution containing formic acid with an HCOOH/Ni mole ratio equal to 1mol/mol.

At the end of the impregnation of the aqueous solution containing formicacid, the catalyst precursor undergoes a heat treatment at 150° C., for2 hours under a stream of air containing 50 grams of water per kilogramof dry air with a flow rate of 1 l/h/g of catalyst, then for 1 hour at120° C. under a stream of dry air.

Catalyst A containing 15% by weight of nickel element relative to thetotal weight of the catalyst is obtained. The characteristics of thecatalyst A thus obtained are reported in table 1 below.

Example 4 Preparation of a Catalyst B According to the Invention [5% byweight of Ni-organic additive:formic acid]

The solution S′ prepared in example 2a is dry impregnated, by adding itdropwise, on 10 g of AL-1 alumina obtained according to example 1.

The solid thus obtained is subsequently dried in an oven at 120° C. for12 hours and then calcined under a stream of dry air of 1 l/h/g ofcatalyst at 450° C. for 2 hours.

The catalyst precursor thus obtained is dry impregnated with an aqueoussolution containing formic acid, with an HCOOH/Ni mole ratio equal to 1mol/mol. At the end of the impregnation of the aqueous solutioncontaining formic acid, the catalyst precursor undergoes a heattreatment at 150° C. for 2 hours under a stream of air containing 50grams of water per kilogram of dry air with a flow rate of 1 l/h/g ofcatalyst, then for 1 hour at 120° C. under a stream of dry air.

Catalyst B containing 5% by weight of nickel element relative to thetotal weight of the catalyst is obtained. The characteristics of thecatalyst B thus obtained are reported in table 1 below.

Example 5 Preparation of a Catalyst C in Accordance with the Invention[15% By Weight of Ni-organic Additive:Glycolic Acid]

The solution S prepared in example 2 is dry impregnated, by adding itdropwise, on 10 g of AL-1 alumina obtained according to example 1.

The solid thus obtained is subsequently dried in an oven at 120° C. for12 hours and then calcined under a stream of dry air of 1 l/h/g ofcatalyst at 450° C. for 2 hours.

The catalyst precursor thus obtained is dry impregnated with an aqueoussolution containing glycolic acid, with a C₂H₄O₃/Ni ratio equal to 2mol/mol.

At the end of the impregnation of the aqueous solution containingglycolic acid, the catalyst precursor undergoes a heat treatment at 150°C. for 2 hours under a stream of air containing 50 grams of water perkilogram of dry air with a flow rate of 1 l/h/g of catalyst, then for 1hour at 120° C. under a stream of dry air.

Catalyst C containing 15% by weight of nickel element relative to thetotal weight of the catalyst is obtained. The characteristics of thecatalyst C thus obtained are reported in table 1 below.

Example 6 Preparation of a Catalyst D not in Accordance with theInvention [No Hydrothermal Treatment for Obtaining the Alumina Support]

The solution S prepared in example 2 is dry impregnated, by adding itdropwise, on 10 g of AL-2 alumina obtained according to example 1a.

The solid thus obtained is subsequently dried in an oven at 120° C. for12 hours and then calcined under a stream of dry air of 1 l/h/g ofcatalyst at 450° C. for 2 hours.

The catalyst precursor thus obtained is dry impregnated with an aqueoussolution containing formic acid, with an HCOOH/Ni ratio equal to 1mol/mol.

At the end of the impregnation of the aqueous solution containing formicacid, the catalyst precursor undergoes a heat treatment at 150° C. for 2hours under a stream of air containing 50 grams of water per kilogram ofdry air with a flow rate of 1 l/h/g of catalyst, then for 1 hour at 120°C. under a stream of dry air.

Catalyst D containing 15% by weight of nickel element relative to thetotal weight of the catalyst is obtained. The characteristics of thecatalyst D thus obtained are reported in table 1 below.

Example 7 Preparation of a Catalyst E not in Accordance with theInvention [No Organic Additive, No Final Hydrothermal Treatment]

The solution S prepared in example 2 is dry impregnated, by adding itdropwise, on 10 g of AL-1 alumina obtained according to example 1.

The solid thus obtained is subsequently dried in an oven at 120° C. for12 hours and then calcined under a stream of dry air of 1 l/h/g ofcatalyst at 450° C. for 2 hours.

Catalyst E containing 15% by weight of nickel element relative to thetotal weight of the catalyst is then obtained. The characteristics ofthe catalyst E thus obtained are reported in table 1 below.

Example 8 Preparation of a Catalyst F not in Accordance with theInvention [No Organic Additive]

The solution S prepared in example 2 is dry impregnated, by adding itdropwise, on 10 g of AL-1 alumina obtained according to example 1.

The solid thus obtained is subsequently dried in an oven at 120° C. for12 hours and then calcined under a stream of dry air of 1 l/h/g ofcatalyst at 450° C. for 2 hours.

The solid thus obtained subsequently undergoes a heat treatment at 150°C. for 2 hours under a stream of air containing 50 grams of water perkilogram of dry air with a flow rate of 1 l/h/g of catalyst, then for 1hour at 120° C. under a stream of dry air.

Catalyst F containing 15% by weight of nickel element relative to thetotal weight of the catalyst is then obtained. The characteristics ofthe catalyst F thus obtained are reported in table 1 below.

TABLE 1 Characteristics of the catalysts A to F Crust Ni content Hydro-Particle thickness/grain in Organic thermal Ni size diameter d_(crust)/crust/total Catalyst Support additive treatment (wt %) (nm) (%) d_(core)Ni (%) A (in AL-1 Formic yes 15 14.1 6.8 5 66 accordance) acid B (inAL-1 Formic yes  5 8 3.8 12 71 accordance) acid C (in AL-1 Glycolic yes15 13.9 4.7 10 70 accordance) acid D AL-2 Formic yes 15 10 <1 1.5  7(not in acid accordance) E AL-1 — no 15 13.7 Homogeneous — — (not indistribution accordance) F AL-1 — yes 15 14.5 Homogeneous — — (not indistribution accordance)

Example 9 Catalytic Tests: Performance in Selective Hydrogenation of aMixture Containing Styrene and Isoprene (A_(HYD1))

Catalysts A to F described in the above examples are tested with regardto the reaction for the selective hydrogenation of a mixture containingstyrene and isoprene.

The composition of the feedstock to be selectively hydrogenated is asfollows: 8% by weight of styrene (supplied by Sigma Aldrich®, purity99%), 8% by weight of isoprene (supplied by Sigma Aldrich®, purity 99%)and 84% by weight of n-heptane (solvent) (supplied by VWR®, purity >99%Chromanorm HPLC). This feedstock also contains sulfur-containingcompounds in a very low content: 10 ppm by weight of sulfur introducedin the form of pentanethiol (supplied by Fluka®, purity >97%) and 100ppm by weight of sulfur introduced in the form of thiophene (supplied byMerck®, purity 99%). This composition corresponds to the initialcomposition of the reaction mixture. This mixture of model molecules isrepresentative of a pyrolysis gasoline.

The selective hydrogenation reaction is carried out in a 500 mlstainless steel autoclave which is provided with a magnetically-drivenmechanical stirrer and which is able to operate under a maximum pressureof 100 bar (10 MPa) and temperatures of between 5° C. and 200° C.

Prior to its introduction into the autoclave, an amount of 3 ml ofcatalyst is reduced ex situ under a hydrogen stream of 1 l/h/g ofcatalyst, at 400° C. for 16 hours (temperature rise gradient of 1°C./min), then it is transferred to the autoclave, protected from theair. After addition of 214 ml of n-heptane (supplied by VWR®,purity >99% Chromanorm HPLC), the autoclave is closed, purged, thenpressurized under 35 bar (3.5 MPa) of hydrogen and brought to the testtemperature, equal to 30° C. At time t=0, approximately 30 g of amixture containing styrene, isoprene, n-heptane, pentanethiol andthiophene are introduced into the autoclave. The reaction mixture thenhas the composition described above and stirring is started at 1600 rpm.The pressure is kept constant at 35 bar (3.5 MPa) in the autoclave usinga storage cylinder located upstream of the reactor.

The progress of the reaction is monitored by taking samples from thereaction medium at regular time intervals: the styrene is hydrogenatedto give ethylbenzene, without hydrogenation of the aromatic ring, andthe isoprene is hydrogenated to give methylbutenes. If the reaction isprolonged for longer than necessary, the methylbutenes are in their turnhydrogenated to give isopentane. The hydrogen consumption is alsomonitored over time by the decrease in pressure in a storage cylinderlocated upstream of the reactor. The catalytic activity is expressed inmoles of H₂ consumed per minute and per gram of Ni.

The catalytic activities measured for catalysts A to F are reported intable 2 below. They are related to the catalytic activity (A_(HYD1))measured for catalyst D.

Example 10 Catalytic Tests: Performance in Hydrogenation of Toluene(A_(HYD2))

Catalysts A to F described in the above examples are also tested withregard to the reaction for the hydrogenation of toluene.

The selective hydrogenation reaction is carried out in the sameautoclave as that described in Example 9.

Prior to its introduction into the autoclave, an amount of 2 ml ofcatalyst is reduced ex situ under a hydrogen stream of 1 l/h/g ofcatalyst, at 400° C. for 16 hours (temperature rise gradient of 1°C./min), then it is transferred to the autoclave, protected from theair. After addition of 216 ml of n-heptane (supplied by VWR®,purity >99% Chromanorm HPLC), the autoclave is closed, purged, thenpressurized under 35 bar (3.5 MPa) of hydrogen and brought to the testtemperature, equal to 80° C. At time t=0, approximately 26 g of toluene(supplied by SDS®, purity >99.8%) are introduced into the autoclave (theinitial composition of the reaction mixture is then 6 wt % toluene/94 wt% n-heptane) and stirring is started at 1600 rpm. The pressure is keptconstant at 35 bar (3.5 MPa) in the autoclave using a storage cylinderlocated upstream of the reactor.

The progress of the reaction is monitored by taking samples from thereaction medium at regular time intervals: the toluene is completelyhydrogenated to give methylcyclohexane. The hydrogen consumption is alsomonitored over time by the decrease in pressure in a storage cylinderlocated upstream of the reactor. The catalytic activity is expressed inmoles of H₂ consumed per minute and per gram of Ni.

The catalytic activities measured for catalysts A to F are reported intable 2 below. They are related back to the catalytic activity(A_(HYD2)) measured for catalyst D.

TABLE 2 Comparison of the performance of the catalysts A to F in theselective hydrogenation of a mixture containing styrene and isoprene(A_(HYD1)) and in the hydrogenation of toluene (A_(HYD2)) Ni° contentCatalyst (% by weight) A_(HYD1) (%) A_(HYD2) (%) A (in accordance) 15175 160 B (in accordance) 5 125 130 C (in accordance) 15 180 175 D (notin accordance) 15 100 100 E (not in accordance) 15 77 75 F (not inaccordance) 15 60 57

This clearly shows the improved performance of the catalysts A, B and Caccording to the invention, compared to catalysts D, E and F not inaccordance with the invention.

The catalyst D has lower activity owing to the use of the support AL-2,the preparation of which does not follow the protocol described in theinvention. The catalysts E and F are prepared on an aluminic supportaccording to the invention but for the catalyst E steps e) and f) werenot carried out and for the catalyst F step e) of adding the organicadditive was not carried out whilst step f) was carried out. In thesetwo cases, the nickel is distributed homogeneously throughout thecatalyst grain. The catalysts E and F consequently have an activity thatis much lower than for catalyst A in terms of A_(HYD1) and A_(HYD2).This is explained by the distribution of the Ni in the crust on thecatalysts A, B, and C which gives them a markedly improved activity inparticular in rapid hydrogenation reactions.

1. A catalyst comprising a nickel-based active phase and an aluminasupport, said catalyst comprising between 1% and 50% by weight ofelemental nickel relative to the total weight of the catalyst, saidcatalyst being characterized in that: the nickel is distributed both ona crust at the periphery of the support, and in the core of the support,the thickness of said crust being between 2% and 15% of the diameter ofthe catalyst; the nickel density ratio between the crust and the core isstrictly greater than 3; said crust comprises more than 25% by weight ofnickel element relative to the total weight of nickel contained in thecatalyst, the size of the nickel particles in the catalyst, measured inoxide form, is between 7 and 25 nm.
 2. The catalyst as claimed in claim1, wherein the nickel density ratio between the crust and the core isgreater than or equal to 3.5.
 3. The catalyst as claimed in claim 1,wherein said crust comprises more than 40% by weight of nickel elementrelative to the total weight of nickel contained in the catalyst.
 4. Thecatalyst as claimed in claim 1, wherein the transition interval betweenthe core and the crust of the catalyst is between 0.05% and 3% of thediameter of the catalyst.
 5. The catalyst as claimed in claim 1,characterized in that the size of the nickel particles in the catalystis between 8 and 23 nm.
 6. The catalyst as claimed in claim 1, whereinthe sulfur content of the alumina support is between 0.001% and 2% byweight relative to the total weight of the alumina support, and thesodium content of said alumina support is between 0.001% and 2% byweight relative to the total weight of said alumina gel.
 7. The catalystas claimed in claim 1, characterized in that the thickness of said crustis between 2.5% and 12% of the diameter of the catalyst.
 8. The catalystas claimed in claim 1, characterized in that the nickel density ratiobetween the crust and the core is between 3.8 and
 15. 9. A process forpreparing a catalyst as claimed in claim 1, which process comprises thefollowing steps: a) an alumina gel is provided; b) the alumina gel fromstep a) is shaped; c) the shaped alumina gel obtained at the end of stepb) is subjected to a heat treatment comprising at least one hydrothermaltreatment step in an autoclave in the presence of an acid solution, at atemperature of between 100° C. and 800° C., and at least one calciningstep, at a temperature of between 400° C. and 1500° C., carried outafter the hydrothermal treatment step, in order to obtain an aluminasupport; d) the alumina support obtained at the end of step c) isbrought into contact with at least one precursor of the nickel activephase in order to obtain a catalyst precursor, e) the catalyst precursorobtained at the end of step d) is dried at a temperature below 250° C.;f) the dried catalyst precursor obtained at the end of step e) isbrought into contact with at least one solution containing at least oneorganic additive chosen from aldehydes containing 1 to 14 carbon atomsper molecule, ketones or polyketones containing 3 to 18 carbon atoms permolecule, ethers and esters containing 2 to 14 carbon atoms permolecule, alcohols or polyalcohols containing 1 to 14 carbon atoms permolecule and carboxylic acids or polycarboxylic acids containing 1 to 14carbon atoms per molecule, the mole ratio between the organic additiveand the nickel being greater than 0.05 mol/mol; g) a hydrothermaltreatment of the catalyst precursor obtained at the end of step f) iscarried out at a temperature between 100° C. and 200° C. under a gasstream comprising between 5 and 650 grams of water per kg of dry gas.10. The process as claimed in claim 9, which process further comprisinga step h) of drying the catalyst precursor obtained at the end of stepg) at a temperature between 50° C. and 200° C. under a gas streamcomprising an amount of water strictly less than 5 grams of water per kgof dry gas.
 11. The process as claimed in claim 9, which process furthercomprising a step e1) of calcining the dried catalyst precursor obtainedat the end of step e), under a gas stream comprising an amount of waterstrictly less than 150 grams of water per kg of dry gas at a temperaturebetween 250° C. and 1000° C.
 12. The process as claimed in claim 9,wherein, in step f), the organic additive is chosen from formic acid,formaldehyde, acetic acid, citric acid, oxalic acid, glycolic acid,malonic acid, ethanol, methanol, ethyl formate, methyl formate,paraldehyde, acetaldehyde, gamma-valerolactone, glucose, sorbitol andtrioxane.
 13. The process as claimed in claim 9, wherein, in step f),the organic additive is formic acid.
 14. A process for the selectivehydrogenation of polyunsaturated compounds containing at least 2 carbonatoms per molecule, contained in a hydrocarbon feedstock having a finalboiling point below or equal to 300° C., said process being carried outat a temperature of between 0° C. and 300° C., at a pressure of between0.1 and 10 MPa, at a hydrogen/(polyunsaturated compounds to behydrogenated) mole ratio of between 0.1 and 10 and at an hourly spacevelocity of between 0.1 and 200 h⁻¹ when the process is carried out inthe liquid phase, or at a hydrogen/(polyunsaturated compounds to behydrogenated) mole ratio of between 0.5 and 1000 and at an hourly spacevelocity of between 100 and 40 000 h⁻¹ when the process is carried outin the gas phase, in the presence of a catalyst as claimed in claim 1.15. A process for the hydrogenation of at least one aromatic orpolyaromatic compound contained in a hydrocarbon feedstock having afinal boiling point below or equal to 650° C., said process beingcarried out in the gas phase or in the liquid phase, at a temperature ofbetween 30° C. and 350° C., at a pressure of between 0.1 and 20 MPa, ata hydrogen/(aromatic compounds to be hydrogenated) mole ratio of between0.1 and 10 and at an hourly space velocity of between 0.05 and 50 h⁻¹,in the presence of a catalyst as claimed in claim 1.